Anatomy of a Rover

In January 2004, Spirit and Opportunity, two identical robotic rovers, entered the martian atmosphere and landed after a seven-month journey from Earth. By the time "Is There Life on Mars?" aired on December 30, 2008, both sojourners had explored their respective landing areas for nearly five years, almost 20 times longer than NASA had planned for at a minimum. The twin rovers have made one intriguing discovery after another, and they appear to be still going strong despite creeping signs of old age. Below, learn more about this hardy pair of robotic geologists and their sophisticated scientific instruments.—Lexi Krock

Mini-TES
The Miniature Thermal Emission Spectrometer is housed inside the heated main body of the MER,
but it uses the rover's long neck as a periscope from which to look out and build a detailed
panoramic image of the surrounding area. With infrared light, Mini-TES penetrates martian
surface dust to create a map of telltale heat signatures from rocks and soil, searching
for types and concentrations of minerals that suggest formation by water.
Mission scientists use data from the Mini-TES and MER's other panoramic cameras to choose
potential scientific targets in the landscape.

Pancam
MER uses its twin Pancams to shoot 360° images of its surroundings, which help mission controllers determine where MER will go to make closer
inspections. MER's pair of panoramic cameras look and function like
eyes. Their resolution and field of view mimic human vision,
making them the most advanced color imaging system ever sent to another planet.
The Pancams can rotate in a complete circle on their long, neck-like mast and
can swing up to 180° up or down. More than a dozen filters allow
for imaging across every possible wavelength of light.

Navcam
One of two kinds of non-scientific panoramic cameras aboard MER, two stereo
Navcams help mission engineers back on Earth get a visual impression of MER's
surroundings in black-and-white. MER navigates on its own part of the time,
making computer-generated decisions about where and how to move about the
martian landscape per mission control's daily set of general specifications.
The Navcam provides engineers with a means of visually tuning in as MER carries
out their commands—though not in real time, because of the tens-of-minutes lag time in sending
and receiving communications between Earth and Mars.

Hazcam
Two pairs of hazard avoidance cameras located at MER's front and back are
designed to support the rover's automated navigation, scanning the immediate
landscape for obstacles that may hinder or damage it. Working in tandem with
the rover's computer software, the Hazcams are one of the keys to MER's ability
to make intelligent choices about getting around hazardous features on the
martian surface. While the rover moves at up to two inches per second on flat,
hard terrain, under automated control with hazard avoidance in action, it can
achieve only about one-fifth of that speed.

Low Gain Antenna
Also called the UHF Relay Antenna, this close-range antenna transmits signals
between MER and two orbiting spacecraft, Mars Global Surveyor and Mars Odyssey,
using technology analogous to that of a walkie-talkie. After Surveyor or
Odyssey receives information from either of the MERs, it will act as a
satellite, relaying information back to Earth using its own communication
system. The MER also sports a smaller UHF antenna (not shown here) whose
express purpose is to relay signals detailing the rover's mechanical health via
the spacecraft satellite network to mission operations.

High Gain Antenna
At its tail end, MER is equipped with a communications dish that can point
itself in the direction of Earth and beam signals directly to the three massive
radio antennas of NASA's international Deep Space Network, located in
California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia.
MER's High Gain Antenna can both send and receive signals related to the
rover's scientific work or its general performance. With this steerable
antenna, MER does not have to move in order to communicate directly with Earth,
which saves precious energy for other tasks.

Solar Arrays
What look like shiny, black wings attached to MER's core body are its main
source of power, a suite of solar panels that can fuel its movements and
recharge its two night-use batteries during the day. The solar arrays were designed to generate about 140 watts of power
for up to four hours per day—plenty of energy for all the rover's functions.
Eventually, however (mission scientists can't predict when), seasonal sunlight changes and a
layer of martian dust that will have settled on the arrays will prevent them
from generating more than about 50 watts per day, too little power for the
rover to drive.

In Situ Instruments
MER carries four scientific tools at the tip of a concealed robotic arm that
can extend to examine an interesting rock or patch of soil. The Rock Abrasion
Tool located here is a powerful grinder that can quickly penetrate a
stone's outer layer, creating a hole two inches wide and one fifth of an inch
deep that is ready to be analyzed by one of the other three tools on the
rover's arm, the Microscopic Imager (MI), the Mössbauer Spectrometer (MS),
or the Alpha-Particle X-Ray Spectrometer (APXS). The MI is a specialized camera
that will create the closest views of martian rocks and soils ever obtained,
highlighting tiny visual details in their compositions that may provide
evidence of ancient waterborne sediments. The MS studies minerals that contain
iron, which is abundant on Mars. Each MS measurement takes 12 hours to
complete but can determine the exact chemical composition of iron-bearing
minerals, which may hold clues to Mars' early environment. The APXS complements
the Mössbauer tool by measuring alpha particles and X-ray emissions in the
same samples, yielding further information about their origin and history.

Rocker-Bogie Mobility System
Each MER has already traveled several thousand feet across the surface of
Mars. Doing one better than the average S.U.V., the rovers will take on the martian
landscape with six-wheel drive plus a specialized suspension system that bends
at its joints instead of using springs. NASA's Jet Propulsion Laboratory
developed this so-called Rocker-Bogie system to allow MER to drive over rocks
or ditches bigger than its 10-inch wheel diameter without overturning, one of
the mission's worst-case scenarios. The rover can withstand tilting of up to
45° in any direction without tipping over.

Warm Electronics Box (WEB)
An insulated container inside MER's undercarriage protects the sensors and
brains of its vital electronics and batteries from extremely cold martian
nighttime temperatures, which can plummet to as low as -157°F
during part of the rovers' journey. With a combination of electrically powered
heaters, radioisotope heaters, and heat from the humming electronics housed
within, the WEB provides a continuously temperate environment for MER's most
sensitive technologies, those incapable of operating below -67°F.

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